[proxy] fixing harmony/proxy.js tests and improving error messages + some drive-by fixes

src/builtins.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/builtins.h"
 
 #include "src/api.h"
 #include "src/api-natives.h"
 #include "src/arguments.h"
 #include "src/base/once.h"
@@ skipping 1781 matching lines @@
       isolate,
       NewTypeError(MessageTemplate::kConstructorNotFunction,
                    isolate->factory()->NewStringFromAsciiChecked("Proxy")));
 }
 
 
 // ES6 section 26.2.1.1 Proxy ( target, handler ) for the [[Construct]] case.
 BUILTIN(ProxyConstructor_ConstructStub) {
   HandleScope scope(isolate);
   DCHECK(isolate->proxy_function()->IsConstructor());
-  DCHECK_EQ(3, args.length());
-  Handle<Object> target = args.at<Object>(1);
-  Handle<Object> handler = args.at<Object>(2);
+  Handle<Object> target;
+  if (args.length() < 2) {
+    target = isolate->factory()->undefined_value();
+  } else {
+    target = args.at<Object>(1);
+  }
+  Handle<Object> handler;
+  if (args.length() < 3) {
+    handler = isolate->factory()->undefined_value();
+  } else {
+    handler = args.at<Object>(2);
+  }
   // The ConstructStub is executed in the context of the caller, so we need
   // to enter the callee context first before raising an exception.
   isolate->set_context(args.target()->context());
   Handle<JSProxy> result;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(isolate, result,
                                      ProxyCreate(isolate, target, handler));
   return *result;
 }
 
 
@@ skipping 620 matching lines @@
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_H(DEFINE_BUILTIN_ACCESSOR_H)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 }  // namespace internal
 }  // namespace v8